The invention relates to a device and a method for axially displacing at least one turbine rotor relative to at least one corresponding turbine stator in a multistage axial turbine.
The efficiency of a multistage axial turbine, in particular with stator and/or rotor synchronization, also called clocking, depends on the axial arrangement of the rotor blades relative to the stator blades. Clocking in turbine stators and turbine rotors means that the respective numbers of blades of the stator or rotor in the grids is the same, and the circumferential position from grid to grid is selected theoretically and experimentally in such a way that optimum turbine efficiency is produced. This optimum turbine efficiency in turn also depends on the axial position of the turbine rotor with respect to the turbine stator.
A clocking or synchronization method is known from European Patent Document EP 0 756 667 B1, in which the wake flow of a first blade grid is guided through a second blade grid with relative movement to the blade leading edge of a third blade grid that is stationary relative to the first, wherein a maximum, circumferential deviation between the wake and the leading edge of ±12.5 percent of the blade pitch is supposed to be permissible.
Additional methods for positioning turbine blade stages are disclosed in German Patent Document DE 100 53 361 C1 and European Patent Document EP 1 201 877 B1.
Moreover, it is known that the efficiency of the turbine may diverge quite a bit from its possible optimum because of construction tolerances, deterioration of turbine components in long-term operation, but also in operating conditions deviating from the design state, for example in the case of partial load/overload or a hot day/cold day.
Finally, turbine noise and the excitation of turbine blade vibrations can be influenced by the undesired axial displacement of the turbine rotor relative to the stator.
The invention is therefore based on the objective of avoiding the above mentioned technical problems of the prior art and making available an adjustment possibility for the distance of the turbine rotor relative to the turbine stator at a standstill and/or in ongoing operation.
The inventive device for axially displacing at least one turbine rotor relative to at least one corresponding turbine stator in a multistage axial turbine has a split turbine shaft with a first axially displaceable shaft half, which is connected via a turbine disc to the turbine rotor and via a torque coupling to the second shaft half. Alternatively, the desired axial displacement can also be achieved by the turbine housing being displaced relative to the turbine rotor, i.e., by the stators being displaced relative to the rotors.
These types of optimized turbine stages can be used in all multistage stationary drives through which air, gas or steam flows for power generation, in ship propulsion, and in the propulsion of land vehicles or aircraft.
By axially displacing the turbine rotor relative to the turbine stator and by regulating this axial displacement, the operation of a turbine is kept at its possible optimum efficiency. For example, in the case of a docked multistage low-pressure turbine for aircraft propulsion with 77000 lbf initial thrust and a bypass ratio of 9, differences between optimum and minimum turbine efficiency of −0.4% to +0.4% are to be expected, i.e., range of 0.8%, if one displaces the rotor in both directions in a range of 4 mm axially relative to the stationary stator. This permits a range in specific fuel consumption of 0.8% and in the turbine inlet temperature of 15° C. to be expected. Operation at optimum turbine efficiency can be assured by the axial rotor displacement and its regulation. In addition, noise and blade vibrations can also be minimized.
An advantageous embodiment of the invention provides for the device to have a sliding stub for axially sliding the two shaft halves over one another. Since the length of the sliding stub limits the displacement path, an initial calculation of the maximum displacement path is meaningful.
An advantageous embodiment of the invention provides for the device to have gearing as the torque coupling. But other positive couplings may also be used in this case as long as they permit axial displacement of the two shaft halves relative to one another.
An advantageous embodiment of the invention provides for the device to have an adjusting chamber. In this case, the adjusting chamber can be a circumferential accommodation for the geared shaft halves (of the hollow turbine shaft) that slide axially over one other, in which a corresponding actuating mechanism is arranged for the axial displacement.
An advantageous embodiment of the invention provides for the adjusting chamber to have a pressure chamber for hydraulic or pneumatic actuation. Oil or fuel for example can be used in this case as hydraulic fluids.
An advantageous embodiment of the invention provides for the device to be actuated mechanically, electromagnetically or piezoelectrically. In this connection, combining the different actuations may be meaningful, for example mechanical actuation with a spring or via lever rod and electromagnetic or hydraulic actuation.
Integrating the function of the device into the function of the fixed bearing of the turbine shaft is also conceivable.
An advantageous embodiment of the invention provides for a displacement path of the split turbine shaft of +4 mm to −4 mm for example for a low-pressure turbine with 77 klbf initial thrust. The displacement path in the cited order of magnitude of +4 mm to −4 mm is expressed as a parameter, which represents the aerodynamic power of a turbine, i.e., identifies its efficiency, and is used as the adjusting and regulating signal.
An advantageous embodiment of the invention provides for a device for regulating the displacement path of the split turbine shaft.
Electronic regulation with a closed control circuit can be provided in this case. In doing so, an advantageous embodiment of the invention provides for sensor devices for recording the actual position of the turbine shaft. With permanently set control parameters for the overall machine such as the rotational speed of the low-pressure and high-pressure shafts, engine pressure ratio, shaft power, net thrust or the like, the efficiency of the turbine is represented by characteristic variables and can be adjusted or regulated by optimizing these variables to the optimum. Such characteristic variables are the ratio of the rotational speeds of the high-pressure and low-pressure shafts, fuel consumption, thrust-specific fuel consumption, shaft-power-specific fuel consumption, exhaust gas temperature, turbine inlet temperature, and the like.
An inventive method for axially displacing at least one turbine rotor relative to at least one corresponding turbine stator in a multistage axial turbine features the following steps:
Determining the actual axial position of the turbine rotor;
Determining the displacement path;
Displacing the turbine rotor.